1331 Inner-retinal components contribute to the a-wave of the ERG of the dark-adapted cat

INNER-RETINAL COMPONENTS CONTRIBUTE TO THE A-WAVE OF THE ERG OF THE DARK-ADAPTED CAT. Robson J.G.1 and Frishman L.J.2 ’ Physiological Laboratory, Cambridge CE2 3EG UK/ 2 College of Optomern/ UniversitY of Houston, Houston. TX 77204 fUSA/ Purpose To determine the extent to which the initial negative wave and its return to baseline (the a-wave) of the flash electroretinogram IERG) can be modelled simply as the sum of a negative photoreceptor component and a positive bipolar-cell component. Method We have examined the time-course of the vitreally recorded a-wave in the urethane-anaesthetised cat and the effect upon it of suppressing the responses of inner-retinal Iamacrine or ganglion) cells either with intra-vitreal injection of n-methyl-oL-aspartate [NMoLA) or by application of a steady adapting background of moderate intensity known to affect mainly responses of inner retina. Resuhs The time-course of the a-wave at times more than about 10 msec after the flash is greatly altered by both NMDLA and adapting backgrounds. The most obvious effect of both procedures, removal of a negative component, occurred not only when the stimulus was weak enough for the negative STR to dominate under normal condidons, but also when the stimulus was strong enough for the rods themselves to contribute directly to the a-wave. However, once the responses of inner-retinal cells had been suppressed, the remaining a-wave could be satisfactorily explained as the sum of photoreceptor and bipolar-cell responses modelled as described by Lamb & Pugh I./. Physiol. 449, ~719, 1992) and Robson & Frishman (Vis. Neurosci. 12, 1995) respectively. Conclusion Inner-retinal components contribute substantially to the a-wave of the dark-adapted ERG. Only when these responses have been blocked pharmacologically, or have been sufficiently reduced by an adapting background, can the initial negative wave of the ERG be simply explained as the sum of photoreceptor and bipolar-cell components. Supwrted by EY0667 1.